Paveen Yaqub, from Manchester, was on board the Mavi Marmara, on which nine people were killed when it was stormed by Israeli commandos on Monday.
She said she was later kicked and abused by two Israeli policemen.
"They were kicking my legs to make me fall and mocking me in Hebrew," she said. "They were trying to take trophy pictures with me and they liked laughing in my face.
"They also searched me but I won't go into that. They took pleasure in humiliating us."
Speaking at Istanbul Airport, where planes full of hundreds of deportees landed on Thursday morning, she said the experience had been "a nightmare".
"We were terrorized for the last few days by the Israeli authorities," she said, visibly shaken and holding back tears. "It was an insane situation. I'm exhausted. I haven't slept for days. I was on hunger strike for the last few hours."
Ms Yaqub said that the Israeli authorities had tried to force her to sign a document written in Hebrew, but she refused.
Sarah Colborne, director of campaigns and operations at the Palestine Solidarity Campaign, was also on board the Mavi Marmara.
Insisting that no one on board the boat was armed, she said the attack was an act of piracy and a "massacre".
At one point, she saw a man being shot dead by an Israeli commando.
"We still don't know how many people were actually murdered because there are still many missing," she said.
"When I was on the upper deck I saw an injured person being brought to the back of the deck being tended to by a doctor and someone who is trained in first aid. He was shot in the head. It was clear it was not some paint ball. It was a bullet." Ms Colborne described scenes of chaos on the ship in the moments after the Israelis boarded.
"As I walked up, the dinghies the Israelis used were bristling with arms. I couldn't even count how many ships there were in the water. It was just literally bristling with ships, helicopters, gunfire. The whole thing was just horrific.
"All I know is that there was gunfire everywhere around." The people on board the ship had no idea that the Israelis might use deadly force, she said.
"We had no weapons. We were on a peaceful humanitarian mission. We knew there might be problems with the Israelis because of the way they treated previous convoys in the past and because of the way they treat the Palestinian people.